1). Field of the Invention
This invention relates to a variable impedance device, components thereof and methods of manufacturing the same.
2). Discussion of Related Art
Variable impedance devices are often used within circuits to control current. For example, in a power circuit such as an electric grid where a current can cause high power breakers to trip resulting in temporary or long-term blackouts, a variable impedance device can be used to limit the over current and maintain power flow in the grid.
A variable impedance device usually includes first and second bus bars, a variable impedance component connected between the leads and a component refrigeration system to cool the variable impedance component to below a critical temperature wherein the variable impedance component becomes superconducting. An over current causes the superconducting variable impedance component to transition rapidly to a resistive state, which subsequently heats the variable impedance component to a temperature above the critical current temperature. The variable impedance component; acts like a fast switch that is thermally latched by the over current condition. This switch, in an electric power grid circuit, can rapidly insert impedance (e.g. resistive, inductive, capacitive or a combination) so that the variable impedance component increases the impedance of the circuit during the over current condition and thereof limits the magnitude of the over current.
A refrigeration system can also be used to cool the bus bars. Both bus bars may for example be immersed in a cryogenic bath that reduces their temperature from atmospheric temperature (e.g., 300K) close to terminals of the bus bars to a temperature closer to the critical current temperature at locations closer to the variable impedance component. Such a bath requires a large amount of cooling power. Such a bath also does not allow for more precise cooling of specific locations on a bus bar, which makes it difficult to precisely engineer materials and component configurations along a length of a bus bar. A bath is also impractical in moving structures such as vehicles or rotating arrangements of the kind found in motors and generators.